Brackish Water Hydrozoans

For more information contact Mariah Meek:

Background and Significance of Study

A suite of four predatory hydrozoan species (Maeotias marginata, Moerisia sp., Blackfordia virginica, and Cordylophora caspia) have invaded and become abundant in the San Francisco Estuary (SFE). Our current level of knowledge regarding the basic biology and ecology of these organisms is alarmingly poor in light of both their possibly negative effect on the SFE ecosystem and the increasing trends in jellyfish blooms around the globe. My research seeks to investigate the potential effects of these species on the SFE ecosystem, to determine the key factors allowing successful establishment and spread of these species, and to predict future effects and spread of the invasions.

Brackish water hydro jellyfish single image Brackish water hydros project image of two water hydrozoans Brackish water hydros jellyfish two image

 This research project involves two interrelated components:

1. Genetic studies:

Marker Development

I developed a suite of microsatellite genetic markers for M. marginata and Moerisia sp. to investigate population genetic diversity and reproductive mode in these invasions. See Meek et al. 2010

Evaluation of clonal diversity and mode of reproduction

Life history characteristics and reproductive strategy may play a significant role in invasion success and spread. Asexual reproduction can confer an advantage during the establishment and spread of an invasive species, as asexually reproducing species can avoid the demographic constraints of small population size during the beginning of the invasion. Additionally, the potential for preservation of co-adapted gene complexes with high phenotypic plasticity and broad tolerance ranges is greater under asexual reproduction. However, asexually reproducing invasive species may sometimes be less successful due to low amounts of genetic variation, limited recombination, and reduced ability to purge deleterious mutations.

In my PhD work, I investigated:

  • The level of genetic diversity in the invasive populations of Moerisia sp. and M. marginata in the San Francisco Estuary
  • The relative contributions of asexual and sexual reproduction to these invasions.

I employed the microsatellite markers I developed (see above) and medusae and polyp samples collected from throughout Suisun Marsh. With this research, I am working to understand how the ability to reproduce both asexually and sexually aids in the establishment and spread of these invasive species. See Meek et al. 2013

2. Laboratory studies to determine feeding rates and ecophysiological characteristics:

Jellyfish and other hydrozoans have proven to be important, yet understudied, predators in marine and estuarine systems. According to the Bad Suisun Bay Hypothesis, invasive species have changed the food web in the brackish water habitats of the SFE. We do not currently understand how the invasive hydrozoans in the SFE fit into the trophic ecology of the estuary. In order to assess their potential impact, it is important to understand the basic feeding biology of these species.

In order to begin to understand the trophic ecology of the invasive hydrozoans in the SFE, in collaboration with Alpa Wintzer, I have conducted a series of experiments to determine potential feeding rates and the factors that impact feeding rates. Our question is

  • How does time to feed and prey density impact feeding rates in M. marginata and Moerisia sp. medusae?
  • Additionally, we have conducted a series of experiments using C. caspia polyps we cultured in the lab to look at the effect of temperature and salinity on growth rates and their combined effect on feeding rates. With this work, we are addressing the following questions:
  • What are the reproductive rates of C. caspia under different temperature and salinity conditions?
  • How do different temperature and salinity conditions affect feeding rates in C. caspia?

We are synthesizing the information gained from this work with field collected gut content data to get a better understanding of what these invasives eat, how much and how fast they can prey upon zooplankton, and what the effects of differing temperature and salinity conditions may have on growth and consumption rates. See Meek et al. 2012.

The expected outcome of this work will be a clearer understanding of the effects of several abundant and novel hydrozoan predators in the system and the role of reproductive mode and genetic diversity in the invasions. Through this work, I will gain a better understanding of what makes these invasives successful and predict how the invasion may spread and adapt in the years to come.